Apocalypse - S1-E4
Revealing mistake: After the piano falls from the ceiling, Ritchie rumbles Eddie's "plan" and kicks him out of the flat. When Eddie is pushed out the front door and down the stairs you can see him falling to begin with, but halfway through he actually stops as if he's kneeling, then ducks out of shot. The sound effects lead us to believe that he's fallen all the way down the stairs and been attacked by a pack of dogs at the bottom.
Apocalypse - S1-E4
Revealing mistake: When Eddie falls through the ceiling playing the piano, it's very obvious from the back that it's a dummy because it wobbles around but is stuck to the seat.
